Malleable disc base for direct infiltration measurements using the tension infiltrometry technique

The correct use of the tension disc infiltrometer requires the membrane of the disc base to be completely in contact with the soil surface. To achieve this contact, a thick layer of sand is commonly placed between the soil surface and the disc base. This paper presents an alternative disc (M DB ), which, by incorporating a malleable membrane, allows direct infiltration measurements without using a contact sand layer. Infiltration curves obtained with this new design in a soil under three different tillage management treatments were compared with the corresponding curves obtained with a conventional disc (C DB ) that uses a contact sand layer. The cumulative infiltration curves measured with C DB were analysed by the differentiated linearization (DL) method, and the corresponding curves obtained with M DB were analysed using both the DL and the cumulative linearization (CL) models. The values of hydraulic conductivity ( K 0 ) and sorptivity ( S 0 ) estimated with C DB were also compared with those obtained with M DB . Finally, the cumulative infiltration curves measured with C DB and M DB were compared with the corresponding modelled function for the respective K 0 and S 0 values calculated with the CL and DL models. The results show that, compared with C DB without a contact sand layer, M DB allows complete soil surface wetting even when non‐smoothed soil surfaces are used. The C DB , which yielded average K 0 values 18% lower than those estimated with M DB , gave the highest values of standard error for the hydraulic parameters calculated. Furthermore, the subjective method employed in the C DB ‐DL technique, which requires the first points of the differential infiltration line corresponding to the sand layer to be manually removed, introduces additional uncertainties in estimating S 0 and K 0 . Comparison between the modelled and measured infiltration curves demonstrates that the DL or CL methods applied to M DB gave excellent estimates of S 0 and K 0 . Copyright © 2012 John Wiley & Sons, Ltd.